Agricultural chemicals such as fertilizers, pesticides, and herbicides, are typically applied to plant crops, soil and/or animals as an aqueous solution. Many agricultural chemicals have an activity that varies with the pH of the solution, in that they may be sensitive to degradation in solutions that are too alkaline or too acidic. Such agricultural chemicals commonly have an optimum agricultural activity in aqueous solutions having a slightly acidic pH range, for example pH 4-6.
When such agricultural chemicals are used in areas where the water supply has a pH unsuitable for the agricultural chemical in question (for example, “hard” waters which may be alkaline), the user or operator typically modifies the pH of the water whereby the agricultural chemical is diluted, so that the water is in an acceptable and preferably optimum pH range to ensure optimum or at least acceptable agricultural activity of the chemical in question. This is effected by adding to the water a suitable adjuvant for adjusting the pH, for example, an acid adjuvant when the water is too alkaline. For most agricultural chemicals which are alkali sensitive or acid sensitive, the optimum or at least acceptable pH range for good agricultural activity of the chemical in question may be obtained from known references in the relevant art (for example, The Agrochemicals Handbook, Hartley, D. and Kidd, H. (Eds.), Royal Society of Chemistry, Nottingham, 1991) or such information may be provided by the manufacturer of the chemical in question.
To prepare an aqueous solution of a pH sensitive agricultural chemical, the pH of the water supply is first measured, and a suitable quantity of adjuvant is added to the water to obtain the desired pH. The user must accordingly be equipped with suitable equipment to test the pH of the water, and the pH of the resultant solution following addition and mixing of the agricultural chemical(s) to the water. Commonly used equipment for testing pH includes, for example, a pH meter and a pH indicator which provides visual colour changes indicative of pH range, such as pH sensitive paper (test strips) or chemicals. However, it is cumbersome and time consuming for the user to perform such operations while in the field. In addition, it may be uneconomical to carry pH testing equipment into the field as pH meters can be expensive, bulky and inconvenient, and pH test strips can degrade and become unreliable upon exposure to moisture or temperature extremes. Also, such pH determinations done in the field are often prone to human error. All of these issues can lead to significant wastage of the agricultural chemicals to be applied, as well as possible overuse and/or overexposure of crops, soil and animals to the agricultural chemicals. Accordingly, it is preferable to avoid such pH determinations or measurements during preparation of the aqueous solution of agricultural chemical(s) (“the agricultural composition”) and to provide automatic identification of the desired pH or an acceptable pH during preparation of the agricultural composition.
Commonly used agricultural chemicals and compositions are known to have negative impacts on the environment. For example, phosphate-based compositions that run off into nearby waterways may cause eutrophication (over-fertilization) of aquatic ecosystems, which typically results in loss of oxygen from the water and concomitant loss of fish populations and other aquatic species. In addition, application of nitrogen- and/or phosphate-based agricultural compositions may cause fertilizer burn (leaf scorch), wherein plant tissues are exposed to localized high concentrations of the agricultural compositions. This causes hypertonicity and dessication of the exposed plant tissues, which results in crop damage and loss. At the same time, increasing public awareness of the negative impacts of such agricultural compositions on crop, soil and animal health, as well as the environment in general, have led consumers to turn increasingly towards agricultural products which are raised and labelled as “organic”, such as crops that have been grown using a minimum of only fertilizers and pesticides that are known to be environmentally friendly, and animals that have been raised on such crops. This in turn has led the agricultural industry to seek out alternative agricultural chemicals that are more environmentally friendly. It is also desirable to find a means to increase the efficacy of existing agricultural compositions and thus reduce the total amount of chemicals applied.
Previously, agricultural compositions in concentrate form, comprising a visual pH indicator and a pH modifying agent, were disclosed in U.S. Pat. No. 5,278,132 and U.S. Pat. No. 5,514,639.
U.S. Pat. No. 5,278,132 disclosed a concentrate comprising a pH modifying agent and a pH indicator for colouring water, which concentrate may be diluted with water and added to a pH sensitive agricultural chemical, having an optimum activity within the range of pH 4-6. The proportions of the pH modifying agent and the pH indicator in the concentrate are such that when the concentrate is diluted to the appropriate concentration with water, and the pH of the resultant solution is modified by the pH modifying agent, the pH indicator indicates visually when the pH of the water is in the range of pH 4.
U.S. Pat. No. 5,514,639 disclosed a concentrate comprising a mixture of a pH indicator for colouring water, an agricultural chemical, and a pH modifying agent for modifying the pH of water with which the concentrate is diluted. The agricultural chemical has an activity that varies with the pH of the water and has an acceptable agricultural activity within a range of pH 4-6. The proportions of the pH modifying agent, the pH indicator and the agricultural chemical in the concentrate are such, that when the concentrate is diluted with an appropriate amount of water, an effective concentration of the agricultural chemical is provided and the pH indicator indicates visually when the pH of the solution is in the range of pH 4-6.
Although the compositions disclosed in both U.S. Pat. No. 5,278,132 and U.S. Pat. No. 5,514,639 provided a simple means for immediate visual identification of an aqueous solution of agricultural chemical being in the optimum pH range, in both cases the preferred pH modifying agent was a phosphate-based buffer system and the preferred pH indicator was methyl red, resorcin blue, 2,5-dinitrophenol and chlorophenol red. Examples of suitable phosphate buffer systems included phosphoric acid, and a conjugate base provided by any one of the following: monoammonium phosphate, potassium phosphate, monoorthophosporic esters and diorthophosphoric esters. However, it is not desirable to have a high concentration of phosphates present within agricultural compositions due to their ability to cause eutrophication and the associated negative impact on the environment. Also, agricultural compositions containing phosphoric acid and phosphates may cause leaf scorch which results in crop damage and loss. Inorganic phosphates and salts have also been found to lack compatibility and reduce the efficacy of a number of pesticides. For example, copper hydroxide-based fungicides lack compatibility with compositions containing phosphates. In the presence of phosphates, copper will form a water-insoluble salt, copper phosphate, which precipitates out of solution. As such, it is desirable to significantly reduce the concentration of phosphates in compositions for agricultural use.
A possible alternative to agricultural compositions containing high levels of phosphoric acid and phosphates could be provided by the use of one or more carbohydrate acid(s) as the pH modifying agent or as a component of the pH modifying agent of the concentrate in the place of an inorganic acid. The inclusion one or more carbohydrate acid(s) of could provide a number of advantages over agricultural compositions comprising phosphates and/or phosphoric acid. Carbohydrate acids typically have smaller dissociation constants (Ka) than phosphoric acid, and thus tend to be weaker acids than mineral acids such as phosphoric acids, which have large dissociation constants. As such, the inclusion of one or more carbohydrate acids in the pH modifying agent could result in a less harmful and corrosive composition. In addition, the presence of the carbohydrate moiety assists in the uptake of pesticides and nutrients in plants and soil microbes that have been treated with the agricultural composition. In addition, a carbohydrate-based pH modifying agent within the concentrate and the agricultural composition prepared from the concentrate could provide an additional nutrient source to treated plants and soil microbes. Carbohydrates are a compatible and effective source of organic nutrients for treated plants and soil microbes, particularly if micronutrients are present in the composition.
However, it has been surprisingly discovered that pH indicators previously used in agricultural compositions such as methyl red, resorcin blue, 2,5-dinitrophenol, chlorophenol red and anthocyanins have low stability when used in conjunction with carbohydrate acids in agricultural compositions and hence are not effective for indicating pH levels in such compositions. In fact, it has been determined that methyl red breaks down with the presence of carbohydrate acids in the agricultural compositions making the colour change ineffectual in a relatively short period of time, particularly when temperatures exceed thirty degrees Celsius.
Accordingly, there is a need for a means for simple and automatic identification of the desired pH during preparation of the agricultural composition, wherein such means is also environmentally friendly to crops, soil and animals. There is a need for such a composition that includes a carbohydrate acid in the pH modifying agent and a pH indicator that is compatible with carbohydrate acids.